1. Field of the Invention
This invention relates to a mower unit having a housing, blades supported in the housing to be rotatable about vertical axes acting as the centers of rotation, cutting edges defined at front edge regions of each blade with respect to a direction of rotation thereof, and lift vanes erected from rear edge regions of each blade with respect to the direction of rotation thereof.
2. Description of the Related Art
In a conventional mower unit noted above, as disclosed in Japanese Patent Laying-Open Publication H7-79629, for example, outer rear edges of each blade are bent upward to define inwardly facing lift vanes extending the more forwardly, with respect to the direction of rotation, the farther away the lift vanes are radially from the center of rotation of the blade. The lift vanes generate air flows with rotation of the blades to transport grass clippings cut by the blades toward a predetermined discharge opening.
Where the grass clippings transported to the discharge opening are thrown away outside the machine, the carrier air flows produced by the lift vanes are used to throw the grass clippings. Where the grass clippings are transported through a duct to a grass catcher disposed at the rear end of the machine, a fan is provided for producing carrier air flows from the discharge opening toward the grass catcher.
However, where, as in the prior art noted above, the lift vanes are formed to face inwardly, the carrier air flows produced by the lift vanes have strong inwardly directed vector components with respect to loci of rotation of the blades. As a result, a large part of grass clippings rotates with the blades without being transported outside the loci of rotation of the blades. The grass clippings cut by the blades cannot be transported easily toward a predetermined discharge opening.
To avoid such an inconvenience, it is conceivable to provide each blade with outwardly facing lift vanes extending the more rearwardly, with respect to the direction of rotation, the farther away the lift vanes are radially from the center of rotation of the blade (i.e. sweep-back vanes), or lift vanes extending perpendicular to the locus of the blade (i.e. level vanes). Where the outwardly facing lift vanes are provided, the carrier air flows produced by the lift vanes have strong outwardly directed vector components with respect to the loci of rotation of the blades (in directions to strike hard against housing walls). This is effective not only to suppress the grass clippings rotating with the blades, but to collect the grass clippings as entrained by the carrier air flows outwardly of the blades. Thus, the grass clippings cut by the blades may be transported efficiently toward a predetermined discharge opening. On the other hand, the carrier air flows produced by the lift vanes collide with vertical walls of the housing adjacent the blades to generate explosive sounds, thereby giving loud noise. Where the lift vanes extending perpendicular to the locus of each blade are provided, the carrier air flows produced by the lift vanes have strong vector components along tangents to the loci of rotation of the blades. Compared with the outwardly facing lift vanes, these vanes can suppress the noise due to the explosive sounds, but are unable to collect sufficiently the grass clippings as entrained by the carrier air flows outwardly of the blades. There is room for improvement in terms of grass transporting efficiency.
An object of this invention is to provide a mower unit capable of transporting grass clippings with improved efficiency while achieving noise suppression.
The above object is fulfilled, according to this invention, by a mower unit comprising a housing, blades supported in the housing each to be rotatable about a vertical axis acting as a center of rotation, cutting edges defined at front edge regions of each of the blades with respect to a direction of rotation thereof, and lift vanes erected from rear edge regions of each blade with respect to the direction of rotation thereof, each of the lift vanes including a first vane portion extending the more rearwardly, with respect to the direction of rotation, the farther away the first vane portion is from the center of rotation, and a second vane portion bent in the direction of rotation from a radially outward end of the first vane portion.
With this construction, a rotation of each blade causes the first vane portion to produce carrier air flows with an outward directivity with respect to the locus of rotation of the blade (i.e. carrier air flows having strong vector components rapidly moving away from the locus of rotation), and the second vane portion to produce carrier air flows with a more inward directivity than the carrier air flows from the first vane portion. (i.e. carrier air flows having strong vector components not so rapidly moving away from the locus of rotation than the carrier air flows produced by the first vane portion).
That is, the carrier air flows produced by the first vane portion collect grass clippings cut by the blade radially outwardly of the blade while suppressing the grass clippings rotating with the blade. In addition, the carrier air flows produced by the second vane portion weaken the outward directivity of the grass clippings collected outwardly. This checks a reduction in the transporting capability due to the grass clippings colliding with vertical walls of the housing located adjacent the blade. Thus, the grass clippings cut by the blade are transported efficiently toward a predetermined discharge opening. Moreover, the carrier air flows from the second vane portion weakening the outward directivity of the carrier air flows from the first vane portion have the effect of suppressing an increase of noise due to explosive sounds produced by the carrier air flows produced by the lift vanes colliding with the adjacent vertical walls, and a reduction in the transporting capability due to leakage of the carrier air flows from the housing which would occur with an increase in the outward directivity. In this way, the grass transporting efficiency is effectively improved while suppressing noise.
In a preferred embodiment of this invention, the housing includes a vacuum plate depending from a ceiling thereof and curved to extend along loci of rotation of the blades. Thus, the vacuum plate suppresses leakage of the carrier air flows to allow the carrier air flows to transport the grass clippings efficiently toward the discharge opening of the housing.
In another preferred embodiment of this invention, the vacuum plate has a downwardly converging profile with a lower end thereof disposed closest to the loci of rotation. With this construction, the carrier air flows generated by the rotating blades are caused to flow along the vacuum plate while flowing toward a large space above the blades. This feature suppresses a reduction in the transporting capability due to leakage of the carrier air flows from under the vacuum plate, and enhances erection of uncut grass to provide an improved grass cutting efficiency. The configuration of vacuum plate to be farther away from the blades as it extends upward promotes the effect of suppressing an increase of noise due to explosive sounds produced by the carrier air flows produced by the lift vanes colliding with the vacuum plate.
In a further preferred embodiment of this invention, the housing defines a glass clippings discharge guide path extending along a common tangent of loci of rotation of an adjacent pair of the blades, the adjacent pair of the blades being rotatable in opposite directions so that air flows generated by the lift vanes thereof substantially agree with a discharge direction. With this construction, the carrier air flows from the two blades are discharged in the same direction through the discharge guide path. Moreover, the second vane portions act to weaken the outward directivity of the carrier air flows from the two blades which would hamper the mutual flows in the discharge guide path. Thus, the grass clippings transported by the carrier air flows toward the discharge guide path are allowed to flow swiftly along the discharge guide path by the combined effect of the carrier air flows merging in that guide path. Even where the grass clippings are transported to a grass catcher disposed at the rear end of the machine, the grass clippings may be transported to the grass catcher without requiring a grass collecting fan to supply carrier air flows for transporting the grass clippings from the discharge opening toward the grass catcher.
Other features and advantages of this invention will be apparent from the following description of the embodiments to be taken with reference to the drawings.